1. Field of the Invention
The present invention relates in general to elastomeric gaskets for thermoplastic pipe joints. More particularly, the present invention is an improved pipe gasket having a dual-purpose tail portion that forms a belling ramp and a compression seal/spigot guide.
2. Description of the Prior Art
Pipes formed from thermoplastic materials including polyethylene and PVC are used in a variety of industries. In forming a joint between sections of pipe, the spigot or male pipe end is inserted within the female or socket pipe end. An annular, elastomeric ring or gasket is typically seated within a groove formed in the socket end of the thermoplastic pipe. As the spigot is inserted within the socket, the gasket provides the major seal capacity for the joint. It is critical, during the installation process, that the gasket not be able to twist or flip since a displaced or dislocated gasket will adversely affect the ultimate sealing capacity of the joint.
Certain of the prior art techniques have involved the use of gaskets which formed xe2x80x9clipxe2x80x9d seals, those seals having a lip portion which was deformed by folding back as the male pipe section was inserted within the female pipe section. Lip seals generally rely upon the internal pipe pressure to provide a sealing effect. In some conditions, these type joints are less than desirable since the lip seal can peel away, allowing leakage through the joint. Particularly, under pulsating pressure conditions, lip seals can provide less than satisfactory results. A sudden decrease in internal pipe pressure can result in contamination of the sealing area and of the pipe interior.
One early attempt to ensure the integrity of pipe joints used under demanding conditions was to provide local reinforcement of the groove portion of the female socket end by means of a heavier wall thickness in this region of the pipe. In some cases, reinforcing sleeves were also utilized. Each of these solutions was less than ideal, in some cases failing to provide the needed joint integrity and often contributing to the complexity and expense of the manufacturing operation.
In the early 1970""s, a new technology was developed by Rieber and Son of Bergen, Norway, referred to in the industry as the xe2x80x9cRieber Joint.xe2x80x9d The Rieber system employed a combined mold element and sealing ring for sealing a joint between the socket end and spigot end of two cooperating pipes formed from thermoplastic materials. In the Rieber process, the elastomeric gasket was inserted within an internal groove in the socket end of the female pipe as the female or belling end was simultaneously being formed. The provision of a prestressed and anchored elastomeric gasket during the belling process at the pipe factory provided an improved socket end for a pipe joint with a sealing gasket which would not twist or flip or otherwise allow impurities to enter the sealing zones of the joint, thus increasing the reliability of the joint and decreasing the risk of leaks or possible failure due to abrasion. The Rieber process is described in the following issued United States patents, among others: U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682.
The Rieber system, with its integrally installed gasket provided a compression seal geometry, rather than relying upon the lip seal systems of the prior art. As the female socket end of the pipe cooled around the previously installed gasket, the elastomeric body of the gasket was compressed between a steel reinforcing ring and the groove formed in the socket end of the pipe. When the mating spigot was installed to make up a pipe joint, further compression of the gasket occurred in a radial direction along an internal compression region of the gasket.
Despite the advances offered by the Rieber process, the compression seal geometry presented problems in certain field applications. In some applications, particularly involving larger diameter pipe, the insertion force needed to install the male spigot end within the mating socket end required a high insertion force which could, on some occasions, cause the gasket to be distorted or displaced.
Another problem with the prior art gaskets is that the geometry of the gasket is such that the metal reinforcing ring used to stabilize the gasket must be small in order to accommodate the complex and often narrow profile of prior art gaskets. Current Rieber seal designs are relatively complicated, especially if they feature lips or slender bulbs for high interference with the spigot (thus high compression seal) and low insertion force. The tail in most prior art gaskets is used only for the belling process, therefor additional material is required to build the other parts of the gasket. Further, in order to provide room for the lip or bulb to flow during assembly, the profile must be relatively high and the size of the reinforcing ring thus restricted by the surrounding parts of the gasket. What is needed is an improved gasket that allows for simpler demolding and less material input, while also allowing for a larger reinforcing ring to be used.
Therefore, it is one object of the present invention to provide an improved gasket for use in bell-ended thermoplastic pipes.
It is another object of the present invention to provide a gasket having a simplified profile for easier demolding.
It is yet another object of the present invention to provide a gasket that provides a large interference with the inserted spigot pipe to thus effectuate a tight seal.
It is yet another object of the present invention to provide a gasket with a low insertion force necessary to insert the spigot pipe.
It is yet another object of the present invention to provide a gasket having space for a large metal reinforcing ring that is between about 40% and 60% the thickness of the gasket.
These and other objects are achieved by providing a pipe sealing gasket designed for receipt within a bell pipe groove, the bell pipe also having an inside surface. The gasket fitted within the groove allows a spigot pipe having an outside surface to be inserted therein to form a continuous pipe joint. The gasket can be best described with reference to a horizontal axis drawn parallel to the central axis of the bell pipe, the gasket comprising a ring shaped elastomeric body which, when viewed in cross section, includes a leading nose region joined to a lower compression region by a spigot ramp. The gasket also has a socket bulb region joined to the leading nose region by a concave section and a tail portion.
The tail portion or the gasket is joined to the lower compression region by a spigot face seal and joined to the socket bulb region by a belling face seal in continuity with a belling ramp. The spigot face seal and lower compression region define an angle xcex1 with respect to the horizontal axis prior to insertion of the spigot pipe. The angle xcex1 approaches 180xc2x0 as the spigot pipe is inserted into the socket end of the bell pipe having the sealing gasket therein. Further, the belling face seal is in continuity with the belting ramp, thus creating a continuous ramp-surface for belling when the gasket is in its belling state on a belling mandrel.
The gasket also has an engaged position that creates a seal between the spigot and bell pipes. In the engaged position, the belling face seal is sealingly engaged with the inside surface of the bell pipe when the spigot pipe is inserted into the socket end of the bell pipe. Further, the spigot face seal is sealingly engaged with the outside surface of the spigot pipe when the spigot pipe is inserted into the socket end of the bell pipe, thus forcing the gasket into its engaged state.
The gasket further includes a metal reinforcing element which runs about the diameter thereof. Also, the concave section of the gasket forms a cavity between the inside surface of the bell pipe groove and the gasket when in the engaged position. Further, the lower compression region can also include at least one annular protuberance for sealingly engaging the outside surface of the spigot pipe. Finally, the gasket has a thickness, and wherein the diameter of the reinforcing element is between about 40% and 60% the total thickness of the gasket.
Additional objects, features and advantages will be apparent in the written description which follows.